MainActivity.kt
package com.example.jetpack
import android.content.Context
import android.graphics.Bitmap
import android.graphics.BitmapFactory
import android.os.Bundle
import android.util.TypedValue
import android.view.View
import android.widget.ImageView
import androidx.appcompat.app.AppCompatActivity
import androidx.constraintlayout.widget.ConstraintLayout
import androidx.constraintlayout.widget.ConstraintLayout.LayoutParams.PARENT_ID
import androidx.constraintlayout.widget.ConstraintSet
import kotlinx.android.synthetic.main.activity_main.*
import java.io.IOException
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// create an image view programmatically and add to layout
applicationContext.createImageView().apply {
// add image view to constraint layout
constraintLayout.addViewTop(applicationContext,this)
// get bitmap from assets folder
setImageBitmap(assetsToBitmap("flowers5.jpg"))
// set image scale type
adjustViewBounds = true
scaleType = ImageView.ScaleType.CENTER_CROP
}
}
}
// extension function to create an image view programmatically
fun Context.createImageView(): ImageView {
return ImageView(this).apply {
layoutParams = ConstraintLayout.LayoutParams(
ConstraintLayout.LayoutParams.MATCH_PARENT, // width
//ConstraintLayout.LayoutParams.WRAP_CONTENT // height
285.dpToPixels(context) // height
)
id = View.generateViewId()
}
}
// extension function to add view top of constraint layout
fun ConstraintLayout.addViewTop(context: Context, view: View){
addView(view)
val set = ConstraintSet()
set.clone(this)
// connect view start with parent start
set.connect(
view.id,ConstraintSet.START,
PARENT_ID,ConstraintSet.START,
5.dpToPixels(context) // margin
)
// connect view top with parent top
set.connect(
view.id, ConstraintSet.TOP,
PARENT_ID,ConstraintSet.TOP,
10.dpToPixels(context) // margin
)
// connect view end with parent end
set.connect(
view.id, ConstraintSet.END,
PARENT_ID,ConstraintSet.END,
5.dpToPixels(context) // margin
)
set.applyTo(this)
}
// extension function to get bitmap from assets
fun Context.assetsToBitmap(fileName: String): Bitmap?{
return try {
with(assets.open(fileName)){
BitmapFactory.decodeStream(this)
}
} catch (e: IOException) { null }
}
// extension function to convert dp to equivalent pixels
fun Int.dpToPixels(context: Context):Int = TypedValue.applyDimension(
TypedValue.COMPLEX_UNIT_DIP, this.toFloat(), context.resources.displayMetrics
).toInt()
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/constraintLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#EDEAE0"
tools:context=".MainActivity" />

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